1. Field of the Invention
This invention relates to a method of painting a surface of a building board being conveyed on a conveyor by means of a spray painting apparatus so that a plurality of colors of gradated or shaded patterns are formed thereon.
2. Description of the Prior Art
Publication No. 6-64750 (1994) of an unexamined Japanese utility model registration application discloses a conventional method of painting a surface of a building board being conveyed on a conveyor by a spray painting apparatus so that a plurality of colors of patterns are formed thereon. In the disclosed method, a plurality of paint supply systems are provided for supplying a plurality of different colors of paints. The paint supply systems are switched in accordance with a predetermined timing so that the different colors of paints are supplied to a single spray gun. The paints thus supplied from the respective paint supply systems are sprayed from the spray gun in accordance with respective timings different from one another. Patterns of a plurality of colors are painted on the surface of a building board which is conveyed below the spray gun on a conveyor.
In the above-described painting method, however, the paints of different colors are mixed together in the spray gun after the paints are switched from one color to another, since the different colors of paints are supplied from the respective paint supply systems to the single spray gun. This disadvantageously renders the colors of the paints different from their original ones. Furthermore, the use of a single spray gun cannot provide an efficient painting work when an article to be painted has a relatively large width, e.g. a building board. This reduces the productivity.